Apparatus for application of powdered materials in electrostatic field

ABSTRACT

Disclosure is made of an apparatus for the application of powdered materials onto an article in an electrostatic field, said apparatus having an electrically insulating housing communicating with a bin, said housing having a rotary screw conveyor disposed inside it, said screw conveyor being made of a dielectric material; said screw conveyor and the housing make up a channel for the supply of a powdered material from the bin to a pulverizer electrode made in the form of two coaxial cylindrical sleeves, one of said cylindrical sleeves being rigidly secured at the outlet end of the housing and having on its inner surface acicular pins arranged radially and pointing with their sharp ends toward an article being coated, whereas the other sleeve is disposed at the outlet end of the screw conveyor and is also provided with acicular pins arranged along the perimeter of the end face of the cylindrical sleeve, parallel to the screw conveyor axis, the sharp ends of said acicular pins pointing toward the article being coated; both said cylindrical sleeves are under an equal electric potential.

United States Patent 1 1 1111 Merkind et al.

3,895,261 [45] July 15, 1975 1 APPARATUS FOR APPLICATION OF POWDERED MATERIALS IN ELECTROSTATIC FIELD [76] Inventors: Zalman Isaakovich Merkind, ulitsa Elkina, 84 V, kv. 27; Evgeny Mikhailovich Mosolov, ulitsa Vagnera, 71, kv. 117, both of Chelyabinsk, U.S.S.R.

[22] Filed: June 3, 1974 [21] Appl. No.: 476,046

Primary ExaminerRonald Feldbaum Attorney, Agent, or FirmSteinberg & Blake [57] ABSTRACT Disclosure is made of an apparatus for the application of powdered materials onto an article in an electrostatic field, said apparatus having an electrically insulating housing communicating with a bin, said housing having a rotary screw conveyor disposed inside it, said screw conveyor being made of a dielectric material; said screw conveyor and the housing make up a channel for the supply of a powdered material from the bin to a pulverizer electrode made in the form of two coaxial cylindrical sleeves, one of said cylindrical sleeves being rigidly secured at the outlet end of the housing and having on its inner surface acicular pins arranged radially and pointing with their sharp ends toward an article being coated, whereas the other sleeve is disposed at the outlet end of the screw conveyor and is also provided with acicular pins arranged along the perimeter of the end face of the cylindrical sleeve, parallel to the screw conveyor axis, the sharp ends of said acicular pins pointing toward the article being coated; both said cylindrical sleeves are under an equal electric potential.

2 Claims, 3 Drawing Figures I the bin.v

, 1 APPARATUS FOR APPLICATION OF POWDERED MATERIALS IN ELECTROSTATIC FIELD The present invention relates to apparatus for the application of protective coatings both in production and field conditions and, more particularly, to apparatus for theapplication of powdered materials in an electrostatic field.

Such apparatus are used, for example. for coating pipes for gas and oil pipelines. I

There is known an apparatus for the application of a protective coating in an electrostatic field. comprising a bin to be filled with a powder. said bin having rotors (electrodes) adapted for rotation therein. High voltage is applied to the rotors. While rotating-the rotors fluff up the powder which is at the same time being charged in the electrostatic field. The-charged powder is directed toward an article to be coated.

The above apparatus for the application of a protective coating in an electrostatic field is disadvantageous in that it possesses a great intrinsic capacitance and thus may become explosive. v

A spark discharge in the interelectrode space ignites the powder-and-air mixture, the discharge energy (W) being determined by the formula:

W /2 U' C I I where U is the corona electrodes energy, and

C is the capacitance of theelectrode-artic-le system. An important disadvantage of the, foregoing apparatus is what is referred to as the separation of powder in the electrostatic field, which impedes the use of multicomponent mixtures, such asepoxy powdered compounds. This imposes stringent requirements uponthe fractional composition of powders.

There is also known an apparatus for the application bin must be cleaned periodically in order to obtain a quality coating. In this apparatus the separation effect is also felt strongly: heavierparticles remain in the bin and impair the apparatus performance.

There is also known an American apparatus for coating large-diameter pipes, wherein powder is transported and mechanically ground by air. Driven by air, the powder is directed to a corona electrode made as a plurality of nozzles arranged in a chamber along the perimeter of a pipe. High voltage is applied to the nozzles. The powder-is air-transported from the bin to a corona electrode (a nozzle), charged therein and applied onto the pipe. Unsettled powder is air-driven back to A disadvantage of the latter apparatus lies in its structural complexity, great air flowrate andthe use of sophisticated equipment for air purification.

[n this apparatus, the ,great air flow. rate accounts for considerable thermal losses, so that the pipe to be coated has to be warmed up to a temperature which is higher than the one required for the formation of the coating.

Also known is an apparatus for producing coatings in an electrostatic field by way of pulverizing fluid and viscous materials, comprising a housing, mounted whereupon is a tank to be filled with acoating material, said tank having a lid, said housing being provided with a screw conveyor, a stirrer and a bowl-shaped electrode, the three latter members having a common drive connected to an electric motor.

After the tank has been loaded with a coating material, the latter is supplied by the screw conveyor to the bowl-shaped electrode. applied whereto is high voltage. The pulverized powder is charged. An air flow produces a spray, whereby the powder is applied onto an article to be coated.

A disadvantage of the latter apparatus resides in the necessity of supplying compressed air which carries away part of the coating material.

In addition, the whole apparatus is made of a'currentconducting material, which leads to additional leakage currents and, consequently, affects the performance of the apparatus.

' It is an object of the present invention to provide an apparatus for the applicationof powdered materialsin an electrostatic field without using compressed air. which would be convenient to operate both in production'and field conditions.

' It isan'other object of the present invention to provide an apparatus which wouldmake it possible to carry out flow-line coating of articles, reduce the explosion-hazards of the coating process and minimize power consumption and leakage currents.

The above objects are attained by providing an apparatus for. the application of powdered materials onto an article in an electrostatic field, having a housing communicating with a bin and provided with a screw conveyor adapted for rotation therein, said screw conveyor and said housing making up a channel for the supply of powdered materials to a pulverizer electrode arranged atthe outlet end of the housing and the screw conveyor and connected to a high-voltage source to produce an electrostatic field, wherein, in accordance with the invention, the pulverizer electrode is made in the form of two coaxial cylindrical sleeves, said sleeves also being coaxial with said screw conveyor, one of said sleeves being rigidly mounted upon the electrically insulating housing and having on the inner surface thereof-acicular pins arranged radially, the sharp ends of said pins pointing toward an article to be coated, the other sleeve being secured at'the outlet end of the screw conveyor, which is made of a dielectric material, and also being provided with acicular pins, their sharp ends pointing toward the article to be coated, said pins being arranged along the perimeter of the screw conveyor end face and parallel to the screw conveyor axis, both said cylindrical sleeves being under the sameelectric potential.

lt is expedient that the cylindrical sleeve, which is rigidly mounted on the housing, have two rows of acicular pins, the spacings between said pins receiving those of and reliable in operation. Powder material compositions are changed without stopping the flow line. As a result, a pipe is coated with a smooth insulating layer of a required thickness.

The proposed embodiment of the apparatus has been tested with regard to both thermoplastic and thermoreactive polymer materials.

Good results have been observed in applying vitreous enamel coatings onto cold pipes with subsequent melting of the powder coating.

The invention will hereinafter be explained in greater detail with reference to preferred embodiments thereof presented in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of an apparatus for the application of powdered materials in an electrostatic field;

FIG. 2 is a schematic diagram of pulverizer electrodes, according to the invention;

FIG. 3 is a front view of FIG. 2. Referring now to the attached drawings, the pro posed apparatus for the application of powdered materials in an electrostatic field (FIG. 1) comprises a housing 1 made of a dielectric material, mounted whereon is a bin 2 for feeding a powdered material to the housing 1. Arranged in the housing I, coaxially with said housing, is a screw conveyor 3 rotated by a drive 4 and intended for metering and supplying the powdered material from the bin 2 to a pulverizer electrode 5. The rate of supplying the powdered material to the pulverizer electrode 5 is determined by the speed of rotation,

diameter and pitch of the screw conveyor 3.

In order to minimize undesirable leakage currents, the screw conveyor 3, like the housing 1, is made of a dielectric material.

Arranged coaxially with the screw conveyor 3 and the housing 1, at the outlet ends thereof, is the pulverizer electrode 5, applied whereto is high voltage, for example, from an electrostatic generator (not shown).

The pulverizer electrode 5 (FIGS. 2 and 3) is made in the form of two coaxial cylindrical sleeves which are also coaxial with the screw conveyor 3. One of these, the cylindrical sleeve 6, is rigidly secured at the outlet end of the housing 1 and has on its inner surface acicular pins 7 arranged radially and directed toward an article to be coated. The acicular pins 7 must also be immersed in the powdered material supplied by the screw conveyor 3.

The other cylindrical sleeve 8 is secured at the outlet end of the screw conveyor 3 and rotates therewith. Arranged along the perimeter of the end face of the cylindrrical sleeve 8, parallel to the axis of the screw conveyor 3, are acicular pins 9 directed toward the article to be coated.

The acicular pins 9 of the cylindrical sleeve 8 are coaxial with the axis ofthe screw conveyor 3, whereas the acicular pins 7 of the cylindrical sleeve 6 are directed at an angle to the axis of the screw conveyor 3. Arranged on the inner surface of the cylindrical sleeve 6 are two rows of the acicular pins 7; disposed between said rows is the cylindrical sleeve 8 with the acicular pins 9.

The proposed apparatus for the application of powdered materials operates as follows. A powdered material is loaded into the bin 2 (FIG. 1). The loading may be carried out both continuously and periodically. The drive 4 is brought into action and starts rotating the screw conveyor 3. The latter supplies the powdered material from the bin 2 along the channel made up by the screw conveyor 3 and the housing I to the pulverizer electrode 5.

Applied to the pulverizer electrode 5 is high voltage from an electrostatic generator or some other highvoltage installation (not shown).

Upon entering the zone of the pulverizer electrode 5, the powdered material is pulverized and charged with the aid of the acicular pins 7 and 9 (FIGS. 2 and 3) of the cylindrical sleeves 6 and 8.

The acicular pins 7 and 9 of the pulverizer 5 have a large area of contact with the powdered material, which accounts for a maximum charge imparted to each particle of the powdered material through direct contact. The charged powdered material interacts with the electrostatic field produced by the pulverizer electrode 5 and the article being coated, for example, an earthed pipe 10; the charged powder is brought into contact with the pipe 10 and forms a dense coating thereon.

Apart from the charge acquired by particles of the powdered material through contact. the proposed pulverizer electrode makes for a still greater charge of said particles due to ion adsorption.

The acicular pins 7 and 9 intensify, due to their sharpened points, charge leakage, which, in turn, intensifies the charging of powder particles and the process of transferring these particles onto the article being coated.

The proposed apparatus makes it possible to coat both warmed-up and cold articles, with subsequent melting of the coating in the latter case.

In addition, the proposed apparatus has made it possible to reduce the intrinsic capacitance of the coating system down to a few picofarads, which, in turn, has made it possible to raise the operating voltage up to kilovolts without intensifying explosion hazards of the coating process.

in order to increase the efficiency of the process, it is desirable that use be made of several housings 1, each provided with a screw conveyor 3, said housings being fed from one or several bins. This will make it possible to obtain multilayer coatings with predetermined properties.

What is claimed is:

1. An apparatus for the application of powdered materials onto an article in an electrostatic field, comprising: a housing made of a dielectric material; a bin communicating with said housing and intended for supplying powdered materials to said housing; a screw'conveyor made of a dielectric material, adapted for rotation in said housing and arranged coaxially with the latter; said screw conveyor and said housing making up a channel for the transfer of powdered materials from said bin; a pulverizer electrode made in the form of two coaxial cylindrical sleeves, said sleeves also being coaxial with said screw conveyor; one of said sleeves being rigidly secured on the inner surface of said housing and having on its inner surface acicular pins arranged radially and pointing with their sharp ends to an article to be coated; the second of said sleeves being secured at the end of said screw conveyor and having acicular pins arranged along the entire perimeter of the end face, parallel to the axis of said screw conveyor, their sharp ends pointing toward the article to be coated; said cylindrical sleeves being under an equal electric potential.

2. An apparatus as claimed in claim 1, wherein said cylindrical sleeve rigidly mounted on said housing has two rows of acicular pins, disposed between which are said acicular pins of the cylindrical sleeve arranged at the outlet end of said screw conveyor. 

1. An apparatus for the application of powdered materials onto an article in an electrostatic field, comprising: a housing made of a dielectric material; a bin communicating with said housing and intended for supplying powdered materials to said housing; a screw conveyor made of a dielectric material, adapted for rotation in said housing and arranged coaxially with the latter; said screw conveyor and said housing making up a channel for the transfer of powdered materials from said bin; a pulverizer electrode made in the form of two coaxial cylindrical sleeves, said sleeves also being coaxial with said screw conveyor; one of said sleeves being rigidly secured on the inner surface of said housing and having on its inner surface acicular pins arranged radially and pointing with their sharp ends to an article to be coated; the second of said sleeves being secured at the end of said screw conveyor and having acicular pins arranged along the entire perimeter of the end face, parallel to the axis of said screw conveyor, their sharp ends pointing toward the article to be coated; said cylindrical sleeves being under an equal electric potential.
 2. An apparatus as claimed in claim 1, wherein said cylindrical sleeve rigidly mounted on said housing has two rows of acicular pins, disposed between which are said acicular pins of the cylindrical sleeve arranged at the outlet end of said screw conveyor. 